I found two maps, from 1904 and 1908, referencing a Middlesex Fells Station on the B&M's Western Route. This is the first I've ever heard of such a station or of a station at this location and a Google search does not bring up any relevant results. The location is at the former Goodyear Ave (Stone Pl/Banks Pl) crossing, between Oak Grove and Wyoming. Did passenger trains actually stop here, perhaps seasonally as a retreat from the city? Two blocks west on Goodyear Ave, you'd reach the trailhead for the Cross Fells Trail. I'm also wondering if it was added to the map erroneously and it was maybe just a freight depot.

The Boston Rubber Shoe Co. owned property on both sides of the Boston and Maine Railroad's Portland Division (Western Route) Main Line in Melrose. A station known as Fells was established there about 1883 to serve the factory. The station building was last used on June 30, 1915 and dismantled the following day. Trains continued to stop there, however, until the factory closed on April 11, 1929 and operations transferred to the Edgeworth plant in Malden. The railroad stop was discontinued about 1929.